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2014FallShotcreteEMag

Nozzleman Knowledge Fig. 6: Worn tip (right) compressor, an air supply line that is too small cannot provide enough air volume to facilitate proper nozzle function. The practice of splitting one 3/4 in. (19 mm) air line to supply both the nozzle and blow pipe, or routing 3/4 in. (19 mm) lines long distances will not provide sufficient air volume to the nozzle. Keep the air compressor lines as short as practical, or use 1 in. (25 mm) or Fig. 5: Cut-down tip wear to oversize within days. A worn tip should never be used during shotcrete placement. Never cut down or modify a nozzle tip. The common practice of “opening” or modifying the tip length to alter the spray pattern will result in unac- ceptable consolidation/compaction of in-place material. Both cut-down and worn tips should not be used for struc- tural shotcrete placement (Fig. 5 and 6). Air Supply Fundamentals for Nozzlemen Nozzlemen must be aware of the strong relationship between air supply components and placement quality. A sufficient volume of dry, oil-free air at the nozzle is a primary requirement to gen- erate satisfactory impact velocity. Both the compressor and air delivery system must be sized to generate sufficient nozzle velocity for the scope of work. The wet- mix process will normally require a minimum of approximately 200 ft3/min (CFM) (6m3/min cmm), depending on the nozzle type, the blow pipe orifice size, and placement volume per hour. Air supply lines must have a large enough diameter to provide adequate air volume to the nozzle. Regardless of the size of the Shotcrete • Fall 2014 51


2014FallShotcreteEMag
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